It is proposed to study the factors influencing serum lipoprotein concentrations in normal and experimentally induced hyperlipemic rats. Regulation of lipoprotein levels is being investigated with specific emphasis on the metabolism of the subunit proteins of the apolipoproteins. Changes in apolipoprotein patterns in different experimentally induced hyperlipoproteinemias are being studied. In conjunction with these studies, the mechanism of action of hypolipemic drugs in the various types of experimental hyperlipoproteinemia is under examination. The synthesis and catabolism of the different lipoprotein classes in normal and hyperlipemic conditions will be studied in these rats. The site of catabolism and the fate of the lipoprotein within the cell will be investigated by radioautography employing both light and electron microscopy.